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death code

n. A routine whose job is to set everything in the
computer --- registers, memory, flags, everything --- to zero,
including that portion of memory where it is running; its last act
is to stomp on its own "store zero" instruction. Death code
isn't very useful, but writing it is an interesting hacking
challenge on architectures where the instruction set makes it
possible, such as the PDP-8 (it has also been done on the DG Nova).
Death code is much less common, and more anti-social, on modern
multi-user machines. It was very impressive on earlier hardware
that provided front panel switches and displays to show register
and memory contents, esp. when these were used to prod the corpse
to see why it died.
Perhaps the ultimate death code is on the TI 990 series, where all
registers are actually in RAM, and the instruction "store immediate
0" has the opcode "0". The PC will immediately wrap around core as
many times as it can until a user hits HALT. Any empty memory
location is death code. Worse, the manufacturer recommended use of
this instruction in startup code (which would be in ROM and
therefore survive).